The present invention refers to mounting of ring members on a shaft, and particularly and particularly to a mounting sleeve for mounting a bearing race ring on a shaft in order to give an improved ability of supporting axial load without slipping on the shaft. The invention also refers to a bearing assembly incorporating such a mounting sleeve.
In recent years, the load carrying capacity of rolling bearings has steadily increased due to improvements of internal bearing geometry, heat treatment and materials. As a consequence thereof, it is today possible to use bearings of smaller size for the same load as earlier required larger bearings, or alternatively, bearings of a certain size are today used for higher loads. A commonly used expression for this development is “down-sizing”.
As structural elements for fitting rolling bearings on shafts it is often used adapter sleeves, withdrawal sleeves or splined sleeves. All those sleeves are comparatively thin-walled, externally tapering steel sleeves with cylindrical bore and usually having an axially extending slot. For larger bearings, and therefore larger sleeves, the material used is cast iron. By pressing the inner race ring of the bearing up on the sleeve, whereby the inner race ring is subjected to expansion, a contact pressure is created which via friction will keep the bearing ring fixed to the sleeve and the sleeve fixed to the shaft.
When a bearing mounted on a sleeve is used as an axially locating bearing, the sleeve will transfer the axial load via friction between sleeve and shaft. By calculating the contact pressure for a given driving up distance for a specific bearing inner race ring, it is possible by estimating the friction coefficient to calculate which axial load a specific sleeve will be able to carry.
In order to estimate in a more simple manner the ability of the sleeve to support axial forces, it is often in bearing brochures referred to a control calculation, where the maximum axial load Famax is shown as Famax=3×B×d [N], where B is the width of the bearing ring in millimeters, d is the nominal bore diameter of the bearing ring in millimeters, and the digit 3 is a constant (N/mm.sup.2). The constant is chosen as an approximation of the friction coefficient, a typical driving up (expansion) of the bearing inner race ring, the modulus of elasticity for a typical bearing steel and an assumption of a typical ring cross section.
As a smaller bearing (motivated from the down-sizing aspect) has a smaller nominal diameter or smaller width or both, a consequence in this respect is that the ability of the bearing to accommodate axial load is decreasing, i.e. there will be a risk that the bearing inner race ring will be displaced from its position, which is not acceptable for a locating bearing.
As an example and based on an old bearing and the basic capacity thereof, it is for instance found that a spherical roller bearing 23256K, having the dimensions d=280 mm, B=176 mm and D=500 mm, is suited for a certain combination of radial and axial load. For the specific example it is assumed that the axial load is 130 kN. With a new bearing, having a higher basic capacity, it is evident that the smaller bearing 23152K having the dimensions d=260 mm, B=144 mm and D=440 mm, should be satisfactory from load carrying aspects.
The Famax=3×B×d for the older bearing will be 147.8 kN, whereas it for the smaller bearing will be only 112.3 kN, i.e. only 76% of the axial load the sleeve of the larger bearing can carry. Therefore the parameters of the mounting sleeve will be the determining factor, and it should be necessary to increase the size of the bearing depending on the sleeve, which will give a more expensive bearing, and the possibilities of down-sizing the bearing assembly will be lost.
A possible manner of compensating this would be to increase the driving up (expansion) of the bearing inner race ring, but this in turn would give the negative consequence of an increase of the ring tension tangentially, resulting in a reduced fatigue endurance for the bearing.